When a base station communicates with a terminal device, there is a multicast transmission mechanism of single-cell point-to-multipoint (SC-PTM). In this transmission mechanism, one base station simultaneously sends a same multimedia broadcast multicast service (MBMS) to a plurality of terminal devices.
In the SC-PTM mechanism, when sending the MBMS to the terminal devices by using the SC-PTM mechanism, the base station sends service control information to the terminal devices on a carrier by using an MBMS point-to-multipoint control channel (MCCH). The service control information usually includes: a service identity of the MBMS and a group-radio network temporary identifier (G-RNTI) corresponding to the MBMS. The G-RNTI is used to indicate a terminal device that needs to receive the MBMS. The terminal device receives the MBMS on the same carrier based on the received G-RNTI by using an MBMS traffic channel (MTCH).
When a terminal device is covered by a plurality of cells, one cell corresponds to one carrier frequency, and different cells correspond to different carrier frequencies. The terminal device can receive an MCCH and an MTCH only on a carrier frequency corresponding to one cell.